Conventionally, for example as stated in Japanese Unexamined Patent Publication No. JP-A-2002-28808 (Patent Document 1) and PCT Japanese Translation Patent Publication No. JP-A-2008-504138 (Patent Document 2) and the like, the processing accuracy of a processing apparatus for cutting, grinding and so on is improved by providing the tool side with an ultrasonic transducer whose rotation is enabled in relation to the main body side, and superimposing, on the tool, that rotational action with the vibration of the ultrasonic transducer. With such processing apparatus, in order to supply drive power to the ultrasonic transducer that rotates in relation to the main body side, a primary power coil and a secondary power coil are arranged in opposition to the rotating parts on the main body side and the tool side, and power is supplied to the tool side from the main body side through utilization of the mutual induction action of these power coils.
Incidentally, an ultrasonic transducer is known to be considered as being equivalent to an electrical circuit that has a resonant frequency. In order to drive the ultrasonic transducer efficiently, drive power is supplied with a resonant frequency or a frequency in that neighborhood. However, in the processing apparatus, the ultrasonic transducer's resonant frequency changes along with changes in temperature in the surroundings of the ultrasonic transducer, changes in temperature in the ultrasonic transducer itself, and changes in the load applied to the tool, etc. Therefore, it was possible that the ultrasonic transducer might not be driven efficiently solely by supplying drive power at a fixed frequency, and there was a possibility of a drop in processing accuracy.
Here, it may be proposed that the tool side is provided with a detection member for detecting the state of vibration of the ultrasonic transducer, and a signal coil is provided on both the main body side and the tool side. By utilizing the mutual induction action of those signal coils, the detection signal from the detection member is transmitted as an electrical signal from the tool side to the main body side, thereby adjusting the supplied power based on the state of vibration of the ultrasonic transducer obtained from that detection signal.
However, when signal coils are placed on the rotating parts of the main body side and the tool side of the processing apparatus where the tool side is rotated in relation to the main body side, in order to maintain the opposing states of the main body side signal coil and the tool side signal coil, it is also necessary to install the signal coil coaxially with the tool side's rotating central axis along with the power coil. Locating the power coil and signal coil coaxially, especially with the signal coil, presents a possibility that the magnetic flux generated by the power coil will penetrate the signal coil and produce noise electromotive force in that signal coil, thus mixing noise in with the electrical signal it transmits.
In order to cope with this type of problem, Japanese Unexamined Patent Publication No. JP-A-11-354348 (Patent Document 3) and Japanese Unexamined Patent Publication No. JP-A-11-313491 (Patent Document 4) propose structures that avoid interference of mutual magnetic paths by enlarging the core component that forms the coil's magnetic path or that avoid interference of the mutual magnetic paths by interposing a non-magnetic material between the coils. However, enlarging the core component in the structures indicated in Patent Document 3 and Patent Document 4 leads to enlargement especially of the tool side. Since the tool side is rotated at high speed, if the tool side is enlarged, there is a possibility that it might be difficult to achieve stable rotation.